Computer signals are made up of a combination of zeroes and ones, and they are often below five volts DC. Voltage noise and voltage transients can disrupt the correct flow of electronic data, even when it is as low as two to three volts. A zero may be one to 1-1/2 volts and a one can be 3-1/2 to five volts. Therefore, two or three-volt system noise can change a zero to a one or vice versa, causing inaccurate data and other electronic problems.
The most effective solution is to prevent noise from entering into the system. Electronic equipment must comply with industry shielding standards to keep noise from getting out as well as getting into the equipment. However, when sensitive electronics are connected, transient voltages and electrical noise can enter the equipment through the shielding. Electrical connections and data cabling allow in harmful signals, which may interfere with correct equipment operation.
Usually, good grounding and bonding methods and isolation of data processing equipment from sources of transient voltage interference and electrical noise are the easiest and best ways to correct transient voltages and electrical noise problems, or to prevent them from happening in the first place.
Isolated grounding is also called single point bonding (SPB). Using this method, all data processing equipment is bonded back to a common point. In this way, all equipment is subjected to the same transient voltage surges. When electronics are held to nearly similar voltages, there should be little or no voltage differences. When done correctly, sensitive electronic equipment interconnected with data cabling will have little or no current flow on the interconnecting cabling, reducing data problems. This method usually provides satisfactory results when sensitive electronic equipment is located throughout a facility. Problems may still result with higher frequency current flow on bonding conductors.
The Canadian Electrical Code, Rule 10-906(8) and (9) permits electronic equipment bonding to be separated from bonding for electrical equipment and raceways. Separate bonding conductors may be installed for receptacles and their outlet boxes. It permits insulated bonding conductors to pass through the supplying panelboards without bonding connections with common bonding to an upstream distribution centre. (This rule may be interpreted differently in some provinces). Single point bonding is the result of taking the bonding of all machines back to a common point upstream.
Where data processing equipment is located in a single area such as a computer room, there may be an even more effective method of bonding equipment. Single point bonding usually works very well when sensitive electronic equipment is distributed throughout a facility. However, when equipment is concentrated in one area, transient voltages and high frequency electrical noise can be even better controlled by using a zero signal reference grid (ZSRG). This method may not be practicable when the equipment is widely distributed.
A commercially available copper mesh grid or the computer room’s raised floor can be used as a zero signal reference grid for equipment bonding. Differences in potential among equipment are eliminated by bonding metallic equipment enclosures to the grid. A zero signal reference grid creates low impedance to high frequency signals and noise of all types, controlling or eliminating high frequency current flow on data cabling between the equipment.
A zero signal reference grid is most effective when data processing equipment is located in one area. Building steel and all adjacent metallic objects such as metal piping, raceways, located within two metres should be bonded to the grid. Sensitive electronic equipment should be bonded to the center of the grid by connections as short as possible with no sharp turns or bends. Heating, ventilating and air conditioning can be connected to the outermost grid conductors. Bonding conductors for sensitive equipment should be at least two metres from building steel or other potential lightning paths. All power supplies should be bonded to the grid. Keep all data and power cables close to the grid.
Transient voltage interference also comes from other systems connected to the same power supply, including transformers and lighting panelboards. Computer rooms usually have their own air conditioning systems. Separate power supplies to data processing and air conditioning systems or other electrical equipment helps prevent electrical interference from cycling equipment.
No matter the circumstances, one should always comply with all Canadian Electrical Code requirements for safe grounding and bonding. There should be no conflict between electrical safety and the methods applied to sensitive electronic equipment.
However, Rule 10-200 Current Over Grounding and Bonding Conductorsdoes give some alternatives when there is unwanted current flow in grounding and bonding. The rule says that: (1) Grounding and bonding should be arranged to avoid objectionable current flow; (2) This does not include temporary situations such as ground faults, etc.; (3) Objectionable current flow may be eliminated by (a) abandoning one or more grounds; (b) relocating grounds; (c) interrupting continuity between grounding conductors; (d) other effective action.
As in past articles, a local electrical inspection authority should be consulted for a more exact interpretation of any of the above.